Preparation of 2, 3-dichloro-1, 3-butadiene by dehydrochlorination of 1, 2, 3, 4-tetrachlorobutane



Jan. 27, 1953 K. c. EBERLY ET AL PREPARATION 0F 2,3-DICHLoRo-1,s-BUTADIENE BY DEHYDROCHLORINATION oF 1,2,5,4TETRACHL0R0BUTANE Filed Dec. 22, 1948 5f IN/ENTOR. enndh, berhj Heber? eid By Patented Jan. 27, 1953 UNITED STATES PATENT OFFICE 2,626,964 PREPARATION or aS-DICHLORQJiJBUTA- -DIENE vB Y vDnrrvDRocHI-.oRllsTA'rroN or 1,2,3;4TETRACHL0R0BUTANE Kenneth C. (Ebony, Akron, and Robert J. Reid,

Canal Fult'omOhio, assignors to The Firestone ,Tire Sav Rubber Company, Akron,` Ohio, a corporation of Ohio Applica-tion December 22, 1948, Serial No."66,646

. "2'Clain'1s.

`This invention urelates to the Ypreparation of 2,3-dichloro-1,'3butadiene by dehydrochlo'rination of `1,2,3,4-tetraehlorobutane.1 H

1,2,3.4tetrach1ory:butaney is generallyy preparedby the reaction of chlorine andbutadiene: CH2 :CHEH t CH2 -l-'2C12iCH2C1LCI-IC1 .CHCLCH2C1 There is' obtained by this reaction about'80`to 90 per cent Aof solid 1,2,SA-tetrachlrobutane and 20 to l per cent l.liquid 1,2,3,4-tetrachlorobutane. The solid'isomer has a melting point of 72to '73 C. and a boiling 'point of'102o C. at 22 mm. The liquid isomer vhas `a melting "point'of 1 C.; boiling'point, 94 C. at 22 vrr`lrlfl.;"`d42, A1.454,' "71.1320, 1.5018. Either isomer or a mixture ofthe isomers may be used in the preparation of 2,3-'di'chlor`o- 1,3-butadiene according to this invention.

It appears that on dehydrochlorination two trichlorobutenes are'first produced, 'and by removal of further 'hydrogenchloride several dichlorobvutadienes kare obtained. According-to this invention 2,3-dichloro-1,34butadiene of high purity is obtained by repression' of that' ty'peofl dehydrochlorination which produces unwanted dichloro-l,3butad ienes. 1

The Ygeneral reaction is illustrated -`diagram matieally below:

oHZcLCHcLCHcLoHiCl l,2,3,4tetrachlorobutane N omoionciooroin. 'omero okoHcHzCi 2,3,4-trichloro-l-butene i 1,2,4itrich1oro-2eb1itene (B. P. 94-7 C. at 100 mln.)

(1' B. P.' 35.5 vand 45.1 C. at

'(B. P. 11s-12o.5 o. atico mm.)

/Yhi low the A route rather than lthe `B route. The production of 1,2,4-trich1oro-2-butene by the B route is unobjectionable because it boils at a much higher temperature than the desired 2,3- dichloro-LS-butadiene and the two compounds can readily be separated by distillation. However, the 1,2- and 1,3-dich1orobutadienes obtained by theB route boil in the same 4general range'as the desired 2,3-dichlorobutadiene and are difficult to separate, and their presence is therefore objectionable. f

vAccording to this invention the purity of the 2,3-dichloro-lfbutadiene product is increased by repressing the dehydrochlorination of the 1,2,4-t1ichloro--2-butene. Suchdehydrochlorination involves rearrangementof theolenic linkage. Thus, according to this invention there is used a dehydrochlorination agent which selectively dehydrochlorinates without rearrangement of the olenic linkage when in the presence of an olen which cannot be dehydrochlorinated without such rearrangement. Stated another way, when added to Ia mixture of trichloro-land `2-buten'es it dehydrochlorinates the 2,3,4-trchloro-l-butene. The nal product contains undehydrochlorinated, high-density 1,2,4-trichloro- 2-butene which can easily be separated from the 2,3dichloro-l-butadiene, and only a small amount of the difficulty separable 1,2- and 1,3- dichloro-lgS-butadienes. Calcium hydroxide is the preferred reagentV for vsuch selective dehydrochlorination.

It is notto be supposed fromthe above 'discussion that the reaction progresses in distinctive stages, all of the tetrachlorobutane `being iirst converted to trichlorobutenes, and then after this is completed all Aof the trichlorobutenes being converted to dichlorobutadienes. vThat is not the case. `The two reactions go forward 'simultaneously. The 'same alkaline reagent is advantageously used to effect dehydrochlorination-in both stages 'of the process.

The first dehydroehlri'ationl step appears to produce but two trichlrobutenes, namely, 2,3,4- trichloro-l-butene andthe highd'ensity 1,2,4- trichlro'-2'butene. The Ysolid tetrachlorobutane isomer yields about 'nine parts of the former trichlorobute'ne toonepa'rt of the latter. The liquid `isomer yieldssomewhat less of the former and somewhat more of the latter.

Ifcalcium hydroxidel is used' as the dehydrochlorination agent Va 'purer 2,3-dichloro-L3- butadiene will be obtained than if sodium hydroxide is employed. Using either reagent, both tetrachlorobutanes are dehydrochlorinated l-to 3 2,3,4-trich-loro-l-butene, and this is dehydrochlorinated to 2,3-dichloro-1,3-butadiene. Dehydrochlorination of either tetrachlorobutane simultaneously produces the 1,2,4-trichloro-2- butene. Lime attacks the 1,2,4-trichloro-2- butene less readily than it does 2,3,4-trichloro-1- butene, but sodium hydroxide attacks either with ease. l,2,4trichloro2butene which is left in the reaction mixture in large amount when lime is used is readily separated from the 2,3-dichlorobutadiene whereas the 1,2- and 1,3-dichlorobutadienes which result from the 1,2,4- trichloro-Z-butene and are present in large amount when sodium hydroxide is used are not. Hence, when lime is used and the 1,2,4-trichloro- 2-butene is attacked to only slight extent, purer 2,3-dichloro-l,S-butadiene is obtained.

The accompanying drawing shows more or less diagrammatically an elevation of equipment used for carrying out the process. The vessel I is a ve-liter, three-necked flask. The flask is topped with a 30-cm. fractioning column 3 (38 mm. diameter). A side arm 4 at the top of the column is provided with a product outlet 5. The side arm is tted with condenser 6 which presents a large cooling surface to gases and liquids which reach the end of this side arm. Cooling water supplied through inlet 'l flows through the inner tube 8 to the bottom of the condenser and then up through the condenser and is discharged through outlet 9. The fractionating column 3 is packed with broken glass tubing or the like. The opening I I is for the introduction of tetrachlorobutane, dehydrochlorinating agent, and polymerization inhibitor to the flask. The iitting at the top of the column is provided with openings the reaction. The opening Il was then closed, the iiash was ushed Well with nitrogen, and then slowly the contents were brought to a boil. The nitrogen flow was decreased to 1/2 cc. per second in order to reduce stack losses. The packing in the column 3 was kept wet with a slurry of phenyl-beta-naphthylamine (polymerization inhibitor) and wetting agent in water introduced through tubes I5 to I8.

A mixture of the desired 2,3-dichloro-L3-butadiene and Water boils at "19 C. The trichlorobutenes and tetrachlorobutanes in the presence of Water boil at higher temperatures. Therefore, as the reaction mixture is heated to cause the reaction to go forward, the thermometer is watched. The 2,3dichlorol,3butadiene, together with whatever small amount of other dichlorobutadienes are formed, rise to the top of the column as they are formed and displace the trichlorobutene vapor which in its turn has displaced the vapor of the higher boiling tetrachlorobutane. When sufficient dichlorobutadiene has been formed to ll the top of the apparatus down to the thermometer bulb, the temperature recorded by the thermometer will drop. When it has dropped to a temperature just above the boiling point of a constant-boiling mixture of water and the 2,3-dichloro-LS-butadiene, e. g. 81-82 C., the valve 20 is opened and condensate is drawn off into the ilask 25. As the temperature rises the valve 20 is closed, and the heating is continued, and the operation repeated as many times as necessary to complete dehydrochlorination of the tetrachlorobutane.

The following table records details of various runs:

Run

C4HCl4 Isomcr Amount of above (gram) Water Used (cc.) Inhibitor in Column (cc.) Time Consumed (Hours) Yield (Per Cent) M. P. of Product (C.), abou Other C4H4Cl2 Present, per cent Yield of C4H5Cla (per cent) for thermometer I3 and four dripping tubes I5, IG, I'I and I3 which are fed with an inhibiting composition through the stopcock I9 from a reservoir I9. The product outlet 5 provided with a valve 20 for opening and closing at will, serves for delivery of condensate. Nitrogen is slowly introduced to the flask through the side arm 22. The receiving flask 25 is provided under the valve 20, A polymerization inhibitor such as phenylbeta-naphthylamine is advantageously placed in the receiver 25 to prevent polymerization of the product collected.

Water and dehydrochlorinating agent were introduced into the vessel through the opening II. The water was introduced first and boiled to expel oxygen and then cooled. Air was expelled from the apparatus by means of nitrogen. Other Y inert gas might be used. Either aqueous sodium hydroxide or a slurry of calcium hydroxide was then introduced through the opening I I, together with the required amount of 1,2,3,4tetrachloro butane and polymerization inhibitor. Either solid or liquid tetrachlorobutane or any mixture of both may be used. It was found advantageous to disperse a small amount of wetting agent solution in the iiask to increase the surface at which the reaction took place and thus speed up In each of the runs 18 grams of phenyl-betanapthylamine was added to the reaction vessel in addition to that indicated in the foregoing table as added to the column through tubes I5 to I8. In Run A, 0.1 gram of a wetting agent, sodium dioctyl sulfosuccinate (Aerosol OT), was added to the vessel; in the other runs 0.2 gram was used. Other wetting agents may be employed. A small amount, less than 2 per cent of polymer formed in the vessel in each run. The trichloro- -butenes tend to hydrolyze, and this caused a loss of up to 2 per cent in each run. The stack losses were considerable.

The relative purity of the 2,3dichloro'"1,3 butadiene obtained in the different runs is shown by the melting points. This product contained as impurity other dichlorobutadiene, mostly 1,2- dichloro-l,3butadiene with some 1,3-dichloro- 1,3-butadiene. The yield of trichlorobutene was almost entirely the undehydrochlorinated 1,2,4- trichloro-Z-butene. Some dehydrochlorination of dichlorobutadienes occurred, but the products were chieiiy gaseous and not recovered.

The organic distillate recovered in the vessel 25 was separated from the water, weighed, and distilled at a reduced pressure of mm. or lower. Several runs were made and diiferent equipment 5 was used. The organic liquid usually started to boil in the neighborhood of 40 C. at 100 mm. The commercially pure 2,3dichloro-1,3buta diene (the amount and boiling point of Which are recorded in the table) was collected at 42 to 45 C. at 10() mm.

Although the reaction is advantageously carried out by intermittent recovery of distillate, as described, other methods may be used. The reuxing temperatures may be varied by maintenance of an artificial pressure. Other polymerization inhibitors may be used, such as diphenylamine, etc. The lime need not be used as slurry, but dispersion leads to more rapid reaction and is recommended for commercial operation.

The terms butane and butene are used herein to refer to n-butane and n-butene.

What we claim is:

1. The process of producing 2,3-dichloro-1,3 butadiene which comprises refluxing a 1,2,3,4 tetrachlorobutane in admixture with aqueous lime slurry until the temperature of a partially segregated zone of the vapors closely approaches 81 C. and collecting condensate formed at this temperature while continuing the refluxing.

2. The process of producing 2,3-dichloro-1,3 butadiene which comprises refluxing a 1,2,3,4

tetrachlorobutane in admixture with lime slurry until the temperature of a partially segregated zone of the vapors closely approaches 81 C., collecting condensate formed at this temperature While continuing the reuxing, thereby causing the temperature of the vapors in this zone to rise, then Without withdrawing condensate continuing the refluxing until the temperature of the vapors in this zone again closely approaches 81 C., and then again drawing off condensate and repeating the cycle.

KENNETH C. EBERLY.

ROBERT J. REID.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,397,134 McMillan NOV. 15, 1921 1,998,442 Carothers et al Apr. 23, 1935 2,445,738 Villert July 20, 1948 FOREIGN PATENTS Number Country Date 171,900 Germany June 18, 1906 

1. THE PROCESS OF PRODUCING 2,3-DICHLORO-1,3BUTADIENE WHICH COMPRISES REFLUXING A 1,2,3,4TETRACHLOROBUTANE IN ADMIXTURE WITH AQUEOUS LIME SLURRY UNTIL THE TEMPERATURE OF A PARTIALLY SEGREGATED ZONE OF THE VAPORS CLOSELY APPROACHES 81* C. AND COLLECTING CONDENSATE FORMED AT THIS TEMPERATURE WHILE CONTINUING THE REFLUXING. 